I just searched for VIN decoding and found some very good information. What I was not able to locate was how the check digit works or how to decode or figure what it means. Anybody have this info?

Basically, it's used to verify the VIN to see if there was an error in it. If one of the digits were mistakenly copied down, the VIN will (most likely) have an invalid check digit. To Joe Schmo, it's pretty useless. But to anyone writing a program to do something with VINs, it's a bit complex but extremely cool.